Conventionally, despite an optical disk is cheap, it has advantages of storing a large amount of data, and further being excellent in storage stability of a disk. Nowadays, compatibility between a ROM disk (Read Only Memory) and this optical disk apparatus is placed emphasis on, because CD-R (Compact Disc-Recordable) and DVD-R (Digital Versatile Disc-Recordable) using an organic dye based medium are often utilized for recording. When storing information in these organic dye based media, reflectance ratio (45% or more) same as the ROM disk is obtained in an unrecorded region, and the reflectance ratio lowers in a recorded region (hereinafter referred to as a mark region) to obtain a sufficient degree of modulation (0.6 or more).
Recording of information onto an optical disk using such an organic dye based medium forms the mark region, for instance, based on a record data signal corresponding to recorded information. Specifically, in a period when the record data signal is high level, the organic dye based medium is irradiated with a laser beam of an intensity at which the mark region can be formed, thereby to form the mark region in a recording layer. While, in a period when the record data signal is low level, the organic dye based medium is irradiated with a laser beam of an intensity at which the mark region cannot be formed (normally, an intensity being lower than that of the laser beam irradiated when reproducing the recorded information, thereby to form a space region in the recording layer.
When the intensity of irradiated laser beam is insufficient or excessive, width of the mark region increases or decreases and lengths of the mark region and the space region vary to form the mark region and the space region which are not correspond to the record data signal, thereby precise reproduction of the recorded information becomes impossible.
Therefore, before recording information on such an optical disk, the intensity of the laser beam is adjusted, and a test information is recorded on an inner-most peripheral portion of the optical disk, followed by reproducing the recorded test information to measure asymmetry (hereinafter referred to as β value). An optimum intensity of the laser beam is calculated, which allows a desired β value to be obtained, and the intensity of the laser beam is set to the optimum intensity to perform recording the information.
However, as this optimum intensity is calculated in a test recording area of the inner-most peripheral portion of the optical disk (hereinafter referred to as PCA), sensitivity in the recording layer is varied in the area excluding this area or distribution in intensity of the laser beam collected on an surface of the optical disk is also varied due to defocus, offtrack, tilt error and so on, resulting in the same condition as the case that light intensity falls. Namely, there are problems that the formed mark region and space region do not correspond to the record data signal and that jitter deteriorates, and thereby the recorded information cannot be precisely reproduced.
Then, for instance, written standards of CD-ROM and DVD-R and Japanese Laid-Open Patent Publication No.H5-144000 disclose a technique of detecting a sum of reflected light of a laser beam for recording which is irradiated on a surface of an optical disk, and correcting intensity of the laser beam (normally, it is called as ROPC) so as to equalize the level of the sum of the reflected light in the vicinity of termination of irradiation of the laser beam for recording to a predetermined level, which is a publicly known technique.
Namely, when the intensity level of the sum of the reflected light is high, formation of the mark region is insufficient, which indicates that the intensity of the laser beam for recording is too low. While, when the intensity level of the sum of the reflected light is low, formation of the mark region is excess, which indicates the intensity of the laser beam for recording is too high. The intensity of the laser beam is corrected so as to conform the intensity level of the sum of the reflected light to an optimum intensity level, thereby enabling constant formation of an optimum mark region.
In the above conventional optical disk recording/reproducing method, the sum of the reflected light of the laser beam for recording is detected and a state of formation of the mark region due to recording is sensed. Whereas, in correlation between the intensity of the laser beam for recording and the sum of the intensity of the reflected light, when the intensity of the laser beam is lower than an intensity necessary for a normal mark formation, variation level in the sum of the intensity of the reflected light is sufficiently large, which indicates a state of formation of the mark region to some extent. However, when the intensity of the laser beam further increases over the intensity necessary for the normal mark formation, the variation level in the sum of the intensity of the reflected light tends to gradually decrease to saturate.
Therefore, even if the intensity of the laser beam actually deviates in the vicinity of the optimum intensity and the formed mark region is off an optimum size, the deviation in the sum of the intensity of the reflected light cannot be sensed accurately and precisely.
However, when irradiating the laser beam for recording onto the optical disk, heat disperses within a recording layer. While, it takes time to form a mark. Therefore, a position on which the laser beam for recording irradiates is a rear end of the mark region which has been formed by the moment. Namely, the mark is formed at an anterior position from the position irradiated actually with the laser beam. Thus, the reflected light of the laser beam for recording becomes a reflected light from the rear end position of the formed mark region while the mark is being formed. At this time, in the case of the optical disk using an organic dye based recording film such as CD-R and DVD-R, the reflected light from the mark region and the reflected light from the space region are different in phase. Thus, in a length direction of the mark region, namely in a tangential direction of a recording track of the optical disk, distribution in intensity of the reflected light from the rear end position of the mark region on the surface of a far field shows deviation with reference to the rear end position of the mark region.
Therefore, this deviation of the distribution of the intensity is called tangential push-pull (hereinafter referred to as TPP). This TPP depends on a phase variation corresponding to a state of formation of the mark region due to recording. On the other words, as the intensity of the laser beam for recording is raised, the phase variation at the rear end position of the mark region increases, and as the intensity of the laser beam is reduced, the phase variation at the rear end position of the mark region decreases. The intensity of the laser beam and the phase variation at the rear end position of the mark region have nearly proportionality relation. Therefore, TPP signal level from the rear end position of the mark region is detected, thereby the state of the formation of the mark region due to the recording can be accurately sensed.
A system of detecting the TPP signal from the rear end position of the mark region, thereby sensing the state of the formation of the mark region due to the recording, followed by determining whether good or bad in a recording state, namely a verification system during the recording is already known and disclosed, for instance, in Japanese Laid-Open Patent Publication No.S59-207436.
Japanese Laid-Open Patent Publication No.H7-29179 discloses a method for controlling recording power with the TPP signal (error signal) during recording power irradiation. However, these prior arts show that whether the recording state is good or bad is possible to detect to some extent with a TPP signal monitor, however they do not show a specific constitution and method how to use the TPP signal during the recording in order to correct appropriately or optimally the recording power or the recording state.
For instance, Japanese Laid-Open Patent Publication No.H7-29179 describes to load the TPP signal normalized through the sum of an amount of the reflected light into a microcomputer and to correct the recording power, however does not describe specifically what TPP signal is used and how it is used for correcting the recording power.
Therefore, these prior arts only describe possibility to determine whether the recording is good or bad with the TPP signal and to perform correction of rough recording condition (power). It is difficult to specifically achieve a precise correction and control of the recording condition of the optical disk performed high density recording.
Namely, there has not been a specific proposal yet about measures to accurately detect with high precision difference between a state of formation of the mark region during the recording and a state of formation in an optimum recording condition and to constantly form an optimum mark region while correcting the recording condition for the intensity of the laser beam and so on for reducing the difference as much as possible.